In recent years, in Low-IF or Zero-IF receivers, there may be a risk that not only an RF signal at a frequency of a desired LO signal but also an RF signal at an odd multiple of the frequency of the LO signal are down-converted into signals having the same baseband frequency. For example, a signal of a WLAN (Wireless Local Area Network) of 2.4 GHz has just a threefold frequency with respect to a TV RF signal of 800 MHz. For that reason, there has been a risk that the signal of the WLAN undergoes crosstalk when the TV signal is received.
For that reason, in the receivers, there has been a demand for setting a value of a harmonic rejection ratio to be larger. The harmonic rejection ratio is a ratio of a down-conversion component from an original desired LO signal frequency to a down-conversion component from a threefold or fivefold frequency of an unintended LO signal frequency.
For example, there is a method of adding three signal paths in which a gain and a phase of an LO signal are shifted, to suppress down-conversion of an RF signal having a threefold or fivefold frequency of the LO signal frequency. However, use of this method has needed a large current in order to provide sufficient performance, and there has been a risk that power consumption is increased.
Further, a resonator mixer has been conceived. The resonator mixer is provided with a parallel LC resonator that is provided immediately subsequent to a switch of the mixer and resonates at a fourfold frequency of that of an LO signal, and suppresses down-conversion of a frequency component having a threefold or fivefold frequency of that of the LO signal, which is included in an RF signal (see, for example, Non-Patent Literature 1).